1. Field of the Invention
This invention relates to a system and process for the continuous inline compounding and extrusion of highly filled, thermoplastic blends. The highly filled blends may be used in the fabrication of compliant carpet backings for both automotive and contract carpet.
2. Information Disclosure
The backsizing of carpets for automotive and contract carpet applications has heretofore independently developed due to the specific requirements for each which were thought to render the fabrication of automotive carpet incompatible with that of contract carpets.
The requisites for the original automotive carpeting were that it had to be moldable, abate noises, have good high temperature aging and good low temperature cracking characteristics, and some flexibility. Compliant blends were not a prerequisite for automotive carpeting and moreover were incompatible with continuous conventional compounding and application methods. The tendencies now, however, are toward more compliant automotive carpeting.
On the other hand, contract carpet requires very different properties and, for example, requires very compliant backing materials to be laminated with compatible precoat blends. which function to yield tuft lock, abrasion resistance, dimensional stability, and other properties either superior to or not required of automotive carpeting.
The systems and blends finding the most application in the contract carpet field have essentially been limited to PVC plastisols. While these blends have many limitations regarding their compounding and application to carpet, they had the advantage of being very versatile in that a wide range of properties and characteristics could be compounded into such blends for both backing and precoating carpets to obtain the above mentioned superior properties without sacrificing the continuity of the process or the ability to form good laminates, including carpeting having dimensional stability. These PVC plastisols could be filled yet incorporated into continuous backing operations since they were liquid at room temperature and fused or solidified upon application of heat. PVC plastisol blends as applied to automotive carpets, however, have many disadvantages, and while such are moldable, in the context of automotive carpet processing, they are ill suited and not practicable since temperatures in excess of acceptable limits are required causing problems such as shrinkage, smoking, and the like.
PVC blends have therefore not been utilized in automotive applications which have typically utilized blends that are solid at room temperature and must be heated and/or worked prior to being suitable for application to carpet. The development of the prior art as it pertains to suitable blends for modern automotive carpeting backings has been set forth from the standpoint of two entities in U.S. Pat. No. 4,191,798 to E.I. DuPont de Nemours and Company and U.S. Pat. No. 4,242,395 to J.P. Stevens & Co., Inc.
The referenced patents claim highly filled blends in conjunction with use to back carpets, claiming presence of filler from 50 to 90 percent (DuPont) and 60 to 90 percent (Stevens); the former essentially containing 4 to 12 percent oil and 5 to 50 percent co-polymer ethylene vinyl acetate (e.g. EVA), the latter, 1 to 15 percent plasticizer (e.g. oils), 1 to 10 percent nonvulcanized elastomeric resin and 5 to 25 percent co-polymer ethylene vinyl acetate. While each patent suggests application to carpet by extrusion, neither of these patents teach the manner in which the blends are to be prepared for extrusion or the form of the materials to be extruded, the manner in which they are extruded, design of the extruder, and the like. Presumably one is left to conventional fabrication and extrusion techniques.
Conventional extrusion techniques are generally directed to the formation of an intermediate stage plasticized granule or pellet. The extrusion art suggests that the extrusion of products such as pipe and the like directly from powdered plastic and even some pelletized plastic often results in the formation of voids and/or pores in the product. Such is said to be caused by various volatile constituents, entrapped moisture, and the like. Some of the art has therefore adopted rather elaborate means to dry the blended components during compounding and extrusion and/or to pretreat various components prior to extrusion or utilize, for example, elaborate venting means during extrusion to try to minimize the presence of volatiles in feed materials or to extract volatiles during extrusion. It is believed such methods are not conducive to high volume continuous commercial operations and notwithstanding elaborate preventive means have generally resulted in unacceptable extrudate, and complicated venting techniques, the latter techniques having been highly susceptible to having plasticated extrudate flow into the venting area with other concomitant undesirable results.
Commercial requirements of high volume extrusion have thus generally required formation of the intermediate stage plasticated granule or pellet prior to extrusion. As recited in U.S. Pat. No. 4,127,635, properly compounded pellets have many advantages over the pulverant form in being more dense, more free flowing, less likely to be contaminated by foreign matter, moisture and the like. The pellets however have to be specially compounded so they remain free flowing during shipment and/or inventorying or storage prior to their being extruded into the final product. This intermediate stage has therefore limited the types of blends suitable for commercial use since, for example, compliant and/or soft blends, tacky blends, and the like would not remain free flowing and therefore such compositions could not be considered for use in conventional commercial extrusion systems.
Still yet a further complicating factor is that economics now require the use of relatively inexpensive blends requiring the addition of more and more filler materials. Fillers particularly conducive to forming carpet backing material are essentially pulverized rock or marble such as calcium carbonate and the like. U.S. Pat. No. 4,191,798 indicates highly filled blends do not flux in Banbury Mixers, suggesting use of special additives and the like in order to even compound such blends. Moreover, the extrusion of highly filled blends normally raises extrusion temperatures to intolerable levels, often above the degradation temperatures of suitable polymers used to make the blend. Additionally, more volatiles and/or moisture tend to be introduced by and/or entrapped in such blends, very often resulting in unsuitable extrudate and return of car loads of such blended materials for recompounding, drying, and the like.
Some authorities such as Werner & Pfleiderer Corporation have suggested that it is now justifiable to have in-house compounding operations, which would eliminate various expenses (e.g. customer compounding costs, shipping, related costs, etc.) in conjunction with operations relating to the intermediate stage approach (e.g. pelletizing of blends prior to extrusion). They suggest a two-stage operation consisting of a co-rotating, twin-screw extruder to provide a flexible compounding system in combination with a single-screw machine (melt pump) for use in conveying highly plasticized materials from compounding extruders to generate sufficient pressures for feeding downstream equipment such as a sheet die. However, these techniques have been directed to highly plasticized materials and have not heretofore been directed to the continuous compounding and extrusion of highly filled thermoplastic blends, generally in excess of about 65 percent rock-like fillers such as calcium carbonate and the like. The present invention evolved only after various innovative techniques were developed by Collins & Aikman in collaboration with Werner & Pfleiderer Corporation to overcome the numerous problems associated with the inline compounding and extrusion of such highly filled blends.